In present days, data communication based on wireless LAN typified by IEEE802.11 is in widespread use. Data communication using wireless LAN is used as signal transmitting means which replaces wired communication using in a personal computer (PC), PC peripheral devices such as printer, hard disk and broadband router, FAX, refrigerator, standard-definition television (SDTV), high-definition television (HDTV), camera, video camcoder, electronic device such as mobile phone, signal transmitting means in an automobile and an airplane and the like; and wireless data transmission is performed between these electronic/electrical devices.
IEEE802.11a, a wireless LAN standard, supports high-speed data communication of a maximum speed of 54 Mbps using the OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, and uses a band of 5 GHz as the frequency band thereof. IEEE802.11b supports high-speed data communication of 5.5 Mbps or 11 Mbps using the DSSS (Direct Sequence Spread Spectrum) scheme, and uses the ISM (Industrial Scientific and Medical) band of 2.4 GHz which can be freely used without radio license. IEEE802.11g supports high-speed data communication of a maximum speed of 54 Mbps using the OFDM modulation scheme and uses, similarly to IEEE802.11b, a band of 2.4 GHz.
A high frequency circuit used in a multiband communication device using such wireless LAN includes: one antenna capable of transmitting and receiving for two communication systems (IEEE802.11a and IEEE802.11b and/or IEEE802.11g) which are different in communication frequency band; and a high frequency switch for switching between a connection with a transmitting-side circuit and a connection with a receiving-side circuit. Using the high frequency switch, switching is performed between the transmitting-side circuit and receiving-side circuit for the two communication systems.
Recently, WiMAX (IEEE802.16-2004, IEEE802.16e-2005 and the like) has been proposed as high-speed radio communication standard which covers a communication distance of several kilometers or so. For example, the use of the standard is expected as a technique for covering “the last one mile” of optical communication. WiMAX uses as the frequency band, three bands of 2.5 GHz, 3.5 GHz and 5.8 GHz. Thus, when a high frequency component is configured which covers all the three frequency bands of WiMAX, or when a high frequency component is configured which covers the three frequency bands in a combination of WiMAX and wireless LAN, path branching must be performed for transmit and received signals of the three frequency bands.
As a technique of branching signals of three different frequencies, for example, a composite LC filter circuit has been disclosed in Japanese Patent Laid-Open No. 2003-8385 (Patent Document 1). Also, a triplexer for branching signals of three different frequencies has been disclosed in Japanese Patent Laid-Open No. 2005-57342(Patent Document 2). According to Patent Document 1, triplexer lines are arranged between filters constituting a triplexer and input/output terminals to modify the triplexer performance.